Radome structures are conventionally used to protect microwave antennas and associated equipment, for example, from the physical environment. It is also often desirable to shield such equipment from externally incident electromagnetic energy which can adversely affect the electrical operating characteristics thereof. Ideally, such a shield structure should be arranged, during operation of the antenna equipment, to be substantially transparent to the energy in the selected frequency range handled by the antenna but should reject or suppress all frequencies outside such selected frequency range.
Further, when the antenna equipment is not operating, such a shield structure should effectively reject or substantially suppress the transmission of electromagnetic energy at all frequencies. The structure acts as an electromagnetic "shutter" which is effectively "open" only to the desired operating frequency band during operation and is "closed" to all frequencies when not in operation.
One particular such radome shutter structure is disclosed in my copending U.S. patent application, Ser. No. 415,260, filed Sep. 7, 1982, and entitled "Electromagnetic Energy Shield". In such structure in the "open" state the radome structure provides a selective band-pass characteristic which permits the transmission therethrough of electromagnetic energy having frequencies within a selected pass-band, usually a relatively narrow pass-band, while energies having frequencies outside the pass-band are effectively rejected. In the "closed" state the structure is arranged to substantially reduce the transmission of energy both within the selected band as well as outside the pass-band.
In some instances, however, it is desirable to provide a relatively wide-band structure rather than the relatively narrow band operation as in the structure described in my previously filed application. For example, such a radome structure may be used with wide-band antennas and may be utilized with antennas which are providing only passive "listening" operations in which, in the non-operating state, it is desirable that the structure be "closed" to all frequencies when the passive antennas are shut off in order to avoid detection.